An entirely reasonable question, but one without any sort of formulaic prescription (as I'm sure you're aware). What follows is merely my opinion, but one with a reasonably large sample size:
Most important factors (all couched within the context of the reputation of your school/program) in a loosely decreasing order:
Clinical Grades
PhD
Board Scores
Pre-Clinical Grades
Other Stuff
This is entirely generic, and after being around for a while and seeing multiple rounds of med school class matches take place as well, you'll see that mitigating circumstances and outliers abound, so much so that the schema above is very flexible. Finding and connecting with a prominent clinician is a simple way to leapfrog the schema to some degree. Ultimately, residency programs in superior clinical departments want residents who can perform well clinically.
As someone at my program recently pointed out, having an MD/PhD is no longer a golden ticket to the most desirable programs in the most competitive residencies (though it still seems to be in the "bread and butter" residencies - medicine/psych/path). There are many MD/PhDs applying to rads/derm/optho/rad onc, and simply having an MD/PhD is not as meaningful as it once may have been. Tanking the boards, for instance, will be a source of anxiety all the way up until match day, even if you manage to find a chair of a department who really wants to help you out (and you won't know how much that means until you match).
Speaking
generally, it seems that people at this program generally don't distinguish themselves in the first two years, still do quite well on the boards, and when they come back to the wards, perform well above average. Maybe 1-3 people per year graduate with AOA. Most people don't do any shadowing/clinical work during their thesis time, but there is plenty of opportunity to do so (one person spent a month working with the neurosurgery team ... he's doing
[email protected] now...) Given the above two paragraphs it seems that people from my program go where they want.
RE: "extracurrics"
This could mean nearly anything, from singing in your schools inevitably medically-themed A cappella group to touring with your signed band. Starting a health policy interest group to working on national legislature. You get the point. If the magnitude of your skill/activity is great, sure, it'll help. If not, it's a conversation piece at best.
In short, it depends. Your program should have information from it's collective experience. Ask people who are in the process now - they'll be able to give you the state of the art, as it applies to your program. Over the years students here have compiled a pretty comprehensive "underground" guide to the process, and organize information sessions about the various transitions/planning. As a result, most people around here don't stress out about the process and just focus on doing what they want to do. If your school doesn't already do that stuff, then suggest it. An MD/PhD is like a post-graduate Montessori school - take advantage of what the older kids know, and I'm sure they'll be more than happy to impart that information.
